(1) Field of the Invention
This invention relates to a product and a process for producing edible low gossypol, high protein cottonseed meal.
(2) Description of the Prior Art
An abundant supply of low cost, high protein cottonseed meal remaining after the extraction of cottonseed oil provides an attractive source of edible protein. However, the use of cottonseed proteins in edible products is rare because of the presence of the toxic gossypol pigments in small pigment glands scattered throughout the cottonseed kernel. The Food and Drug Administration, HEW, permits cottonseed products used for human consumption to contain a free gossypol content not to exceed 0.045% (see Federal Register, Vol. 39, No. 177, page 32735, Sept. 11, 1974). Solvent extracted cottonseed meals often have a free gossypol content of 1-1.5% or more, and the liquid cyclone process (LCP) underflow cottonseed meals, 2.5% or more. Before the gossypol pigments can be extracted from the cottonseed meal, it is necessary to effectively rupture the pigment glands. Cottonseed meal processed by the LCP route has been dried to a moisture level of about 1.5% in order to toughen the pigment glands. Rupture of the toughened glands in the LCP underflow cottonseed meal is difficult, and thus, extraction of the gossypol pigments to a level of free gossypol acceptable for food use, is more difficult to obtain.
Over a period of a number of years there has been a marked interest in the improvement of the nutritive value of cottonseed meals. The U.S. Pat. No. 2,726,155 discloses a method for treating soybean and cottonseed meals with 20-50% water, adjusted to either an acid or alkaline pH, followed by mixing and heating to dehydrate the meal, thereby increasing the soluble nitrogen content and, consequently, the nutritive value of the meal. Although it is suggested that compounds could be added to the aqueous phase to react with gossypol and/or other components in the meals, detoxification or removal of free gossypol is not included in this method.
Pre-extraction of pigments, including gossypol, from full fat glanded cottonseed flakes with methanol containing 2.5% soap prior to the extraction of the oil by hydrocarbon is described in U.S. Pat. No. 2,485,916. The purpose of this invention is to obtain a high yield of oil of a purity comparable to that obtained from expensive refining procedures. No mention is made in this invention as to the level of free and bound gossypol pigments present in the solvent-extracted cottonseed meal.
Detoxification of defatted glanded cottonseed meal, after adjustment of the pH to between 7 and 10 with aqueous sodium hydroxide and adjustment of the moisture content to between 5 and 14%, by extraction with hot 2-propanol is described in U.S. Pat. No. 2,873,190. Free gossypol is reduced to 0.04% by a single extraction with hot 2-propanol, and 0.01% after multiple extractions. No data are given as to the levels of bound gossypol present in the cottonseed meal treated and extracted as described treatment ruptures the pigment glands, releasing gossypol and related pigments that rapidly combine with cottonseed meal constituents to form non-toxic "bound" derivatives. It is known that gossypol combines with epsilon aminolysine to lower the nutritive value of the cottonseed meal.
A process for the detoxification of defatted cottonseed meal by reacting the free or unbound gossypol pigments with organic primary amines is described in U.S. Pat. No. 2,934,432. The reaction product and the unreacted amine are removed by extraction with a non-polar solvent. The free gossypol content in the cottonseed meal was reduced from 1.4% to 0.002% by this process.
Preparation of cottonseed meal suitable for unrestricted use in laying hen diets by a process in which the gossypol in cottonseed meats, prior to removal of oil, is chemically modified without causing detrimental changes in cottonseed protein and, thereby, producing a feed that does not cause hen eggs to become discolored on storage, is described in U.S. Pat. No. 2,873,191. Full fat cottonseed flakes are increased in moisture content to about 74% at an alkaline pH and reacted with fatty amine at 125.degree. F. for 30 minutes with stirring, to rupture the gossypol glands, after which the heating rate is increased, causing the temperature of the material to reach a final temperature of 212.degree. F. in approximately 30 minutes, during which the fatty amine reacts with the free gossypol. After cooling to ambient temperature the oil is extracted from the treated cottonseed meat with a liquid hydrocarbon. The resulting cottonseed meal contains less than 0.010% free gossypol.
A similar process is described in U.S. Pat. No. 2,607,687 wherein the free gossypol pigments present in defatted cottonseed meal are reacted with aniline in the presence of additional water and heat to form dianiline gossypol. Excess aniline is removed by steam distillation. The resulting animal feed is of improved color and nutritive value, with a free gossypol content of 0.015%-0.04%.
The analine process cottonseed meal was in commercial use in the 1950's marketed as degossypolized meal and later as low gossypol cottonseed meal. However, in view of the results from animal feeding tests, which showed enlarged organs, including the spleen, the product was removed from the market. The process utilizing the detoxification of gossypol by reaction of organic primary amines with free or unbound gossypol pigment has not been commercialized.
An acetone-hexane-water extraction process for the removal of free or unbound gossypol pigments from defatted cottonseed meal is described in U.S. Pat. No. 2,950,198. This process effectively removes free gossypol pigments to a level of 0.00-0.040%.
Aqueous acetone extraction of free or unbound gossypol, as well as aflatoxins (toxic mold metabolites) from cottonseed followed by hexane extraction of the cottonseed oil is described in U.S. Pat. No. 3,557,168. Free gossypol levels of the extracted cottonseed meal average 0.020%.
The two above mentioned procedures have not been commercialized because of unpleasant flavor and odor problems brought about by reactions of acetone condensation product "mesityl oxide" breakdown products of sulfur-containing amino acids to provide a "catty odor." Fore etal JAOCS 52 (3) 84-87 (1975). Also, problems with adaptation of the axeotrope process to commercial practice have lead to a lack of interest in this approach.
Production of an edible cottonseed protein concentrate from cottonseed is described in U.S. Pat. No. 3,615,657 and No. 3,972,861, wherein the cottonseed meats are dried to a moisture level of 1.5-2.5%, comminuted in a mill, and processed in a liquid cyclone with hexane to separate the cottonseed into an overflow fraction essentially free of gossypol glands with a free gossypol content of 0.03-0.04%, an underflow fraction containing gossypol glands, hulls, seed fragments, etc., and the hexane containing the extracted cottonseed oil. The liquid cyclone process produces a cottonseed protein concentrate of acceptable flavor and free gossypol content. However, 60-65% of the processed cottonseed is contained in the underflow fraction, which is extremely high in free gossypol and can be used for livestock feed only. In addition, the liquid cyclone process requires special equipment for implementation.
A method for processing glanded cottonseed for protein and oil using acetic acid-hexane mixtures to more effectively separate the oil from cottonseed is described in U.S. Pat. No. 3,941,764. Relatively few gossypol pigment glands were disrupted by the solvent-acid mixtures although the amounts of gossypol pigments in the miscella increased as the concentrations of acetic acid in hexane increased. The addition of 2% and 4% acetic acid to the hexane did not affect the solubility of the protein of the neutralized extracted cottonseed meal in 0.02 N sodium hydroxide. Addition of 10% acetic acid to hexane denatured the protein somewhat and the protein solubility was reduced to 91.3%. The cottonseed meal produced by this process, however, is high in free gossypol inasmuch as the gossypol remains in the intact pigment glands.
The extraction of cottonseed flours with solvent mixtures containing a non-polar solvent, a polar solvent, water and a food grade acid to prepare protein isolates of improved color, is described in U.S. patent application Ser. No. 943,893, filed Sept. 19, 1978. The described solvent mixture when used to extract the liquid cyclone process cottonseed flour concentrate does not appreciably reduce the free and total gossypol content of the extracted concentrate.